Session Initiation Protocol Automatic Debugger

This paper aims to propose a session initiation protocol (SIP) automatic debugger tool. It is a software instrument that will be used to verify the compliance of voice over Internet protocol (VoIP) devices, such as soft phones and VoIP gateways to the SIP specifications, and to test the interoperability of VoIP equipment produced by different manufacturers. Different tools are available on the market to conduct a compliance and interoperability validation phase. However, they often have features limited to packet capturing and decoding, or they are simulation tools that often require a complex developing phase to define the behavior of each test. The proposed tool, instead, can be inserted into an SIP network and is capable of observing and analyzing, in an automatic way, the communication steps. It operates by executing three subsequent phases. In the first phase, the SIP messages flowing in the network are captured. Then, a second phase is in charge of grouping SIP messages into transactions and dialog. Finally, a third phase operates by comparing the message flow with a set of predefined rules. Rules have been classified in two groups. Rules belonging to the first group, called static rules, have been obtained by the direct analysis of SIP specifications. Rules belonging to the second group, called dynamic rules, have been obtained by experience with SIP compliance and interoperability testing (with the support of SIP testing experts). When verification of some rules fails, an output is reported by indicating the rule that failed and a list of possible fault causes. The tool has been validated in a laboratory network in different scenarios. Some sample test cases, which have been extracted by these scenarios and show the capability of the SIP automatic debugger tool in finding compliance and interoperability faults, are also presented in this paper.